This invention relates to the field of methods for automatically characterizing and/or identifying a microbial agent present in a sample, such as blood or other biological sample, stored in a specimen container. As an example, the methods of this disclosure provides information as to Gram type (positive or negative), morphology, species or other relevant clinical information of the microbial agent rapidly and automatically.
Instruments currently exist on the market in the U.S. that detect the growth and therefore the presence of a microorganism in a blood sample. One such instrument is the BacT/ALERT 3D instrument of the present assignee bioMérieux, Inc. The instrument receives a blood culture bottle containing a blood sample, e.g., from a human patient. The instrument incubates the bottle. Periodically during incubation an optical detection unit in the incubator analyzes a colorimetric sensor incorporated into the bottle to detect whether microbial growth has occurred within the bottle. The optical detection unit, specimen containers and sensors are described in the patent literature, see U.S. Pat. Nos. 4,945,060; 5,094,955; 5,162,229; 5,164,796; 5,217,876; 5,795,773; and 5,856,175, the entire content of each of which is incorporated by reference herein. Other prior art of interest relating generally to the detection of microorganisms in a biological sample includes the following patents: U.S. Pat. Nos. 5,770,394, 5,518,923; 5,498,543, 5,432,061, 5,371,016, 5,397,709, 5,344,417, 5,374,264, 6,709,857; and 7,211,430.
In detection instruments such as the BacT/ALERT 3D and similar instruments, once the blood culture bottle has been tested positive for microorganism presence, it is difficult to obtain a high level of characterization of the microbial agent, or identification of the species of the microbial agent, due to the interference of blood components and artifacts of the disposable system (e.g., bottle) containing the sample. Therefore, current methods use a bottle or other suitable disposable container and a related instrument for natural growth and detection of a microorganism in the sample, as described above. Once the instrument indicates that the bottle is positive for presence of a microbial agent, according to current methods the “positive” bottle is manually retrieved from the instrument and a portion of the sample is manually removed from the bottle and cultured on an agar plate. There are instruments in the art that automate the streaking of a sample medium on a culture plate and incubating the plate. One such instrument is described in U.S. Pat. No. 6,617,146. After streaking, the plate is manually placed in an incubator and periodically inspected for growth of a subculture of the microorganism. After the subculture has grown sufficiently, a sample of the culture is taken from the plate and placed in a test tube. The test tube is then introduced into yet another instrument for identification testing via a disposable test sample card having a multitude of individual wells. The disposable test cards are known in the patent literature, see e.g., U.S. Pat. Nos. 4,118,280, 3,963,355, 4,018,65; 4,116,775 and 4,038,151, 5,609,828, 5,746,980, 5,766,553, 5,843,380, 5,869,005, 5,916,812, 5,932,177, 5,951,952, and 6,045,758, the entire content of which is incorporated by reference herein.
The test sample card is then processed in an analytical instrument known in the art as the VITEK 2 instrument of the assignee. The VITEK 2 instrument incubates and periodically reads the wells of the test sample card with a reader unit. Growth of the sample in one or more of the wells of the cards results in identification of the microbial agent. The VITEK 2 instrument is described in the patent literature, see e.g., U.S. Pat. Nos. 5,762,873 and 6,086,824, the content of which is incorporated by reference herein.
This entire process from the time of introducing the sample into the blood collection bottle to culture, detection of microorganism presence, and then identification of the microorganism by the VITEK 2 instrument typically takes 2-5 days. The identification steps alone, occurring after positive bottle detection, typically occupy 1-3 of these days.
Substantial, and potentially life saving, clinical benefits for a patient are possible if the time it takes for detection and identification of a microbial agent in a blood sample and reporting the results to a clinician could be reduced from the current 2-5 days to less than one day. This document discloses a method for rapid identification and/or characterization of a microbial agent in a biological sample such as a blood sample using a taxonomical hierarchical classification method.